One of the main purposes of hydraulic accumulators is, among other things, to accommodate certain volumes of pressurized fluids of a hydraulic system and to feed these volumes back to the system upon demand. Hydraulic accumulators of this type that are in common use include piston accumulators, bladder accumulators, diaphragm accumulators, and weight-loaded and spring-loaded accumulators. Hydraulic accumulators of this kind can be used to perform a variety of tasks, such as storing energy, damping shock, oscillation and pulsation, recovering energy, compensating for volume flow, etc.
Valve control units that are commonly equipped with on-off or way valves to control the flow of fluid to and from the hydraulic accumulator are used to operate the hydraulic regulators and control them. In this connection, the hydraulic accumulator is commonly connected to pipework or fluid conduits by fluid lines that provide the fluid-carrying connection between the accumulator and the valve control unit. Drawbacks of the known solution, as embodied in a wide variety of designs that are readily available on the market, include sealing problems caused by the large number of connections between the hydraulic accumulator pipework and the valve control unit and by the added costs for the network of lines connecting to the fluid lines. Especially under cramped conditions, there are also problems with accommodating the large number of the above-mentioned components in a reasonable fashion and connecting them together in such a way that they can carry fluid. Since different manufacturers produce the hydraulic accumulators, the pipework, and/or the valves of the valve control units, mating problems arise at the site where the installation work is actually done.
DE-A-27 07 469 discloses a hydraulic accumulator, especially in the form of a device for regulating pressure. This known hydraulic accumulator accomplishes the tasks of keeping the pressure in the accumulator at a given level and protecting the accumulator against any accidental overpressure. To accomplish these tasks, the hydraulic accumulator has a valve slider, like a hollow sleeve, located inside a valve recess extending along the longitudinal axis of the hydraulic accumulator. The valve slider receives the high pressure at its middle. At one of its ends, the valve slider is subjected to the operating pressure to be regulated. At its other end, the valve slider rests against a support body on which an adjustable spring exerts a counteracting force. Since the surface area of the contact circle between the sleeve and the support body is smaller than the surface area of the cross-section of the sleeve itself, the displacements of the sleeve against the spring cause the inlet opening through which the high pressure enters to close like an on-off valve. This known valve arrangement is an integral part of the lower half of the housing of the accumulator. The lower half can be screwed together with the upper half of the housing, thereby forming the housing of the hydraulic accumulator. With the known solution, the separating element includes an elastic-rubber diaphragm equipped with a closing unit in the middle, so that the switching direction of the on-off valve coincides with the direction of motion of the separating element. If the on-off valve fails in this known solution, for maintenance purposes, the valve block that contains the on-off valve has to be removed together with the lower half of the housing or the appropriate replacement has to be made. This requirement increases the production and maintenance costs in the known solution. Although the valve control unit with the known on-off valve is designed to be large in terms of geometry, only one valve function can be performed in terms of triggering the separating element.
For a piston pressure accumulator, especially for drive-slip-controlled braking systems, DE-A-39 41 241 discloses an on-off valve in the form of a load valve. To save space, the valve direction of motion is arranged perpendicular to the direction of motion of a pressure accumulator piston, as well as to the direction of motion of a shaped part that surrounds it as a partition unit for the accumulator. This piston is placed above a monitoring switch, as a motion sensor for the shaped part in a valve block of the valve control unit of the piston pressure accumulator. With this known arrangement, however, only a single switching task is accomplished. Since the on-off valve is installed in a transverse position, the valve control unit still requires a relatively large amount of room. Moreover, the transverse installation position makes it necessary to divert the fluid stream, which is undesirable from the standpoint of fluid mechanics.
EP-A-0 816 142 and U.S. Pat. No. 5,342,080 disclose hydraulic accumulators. These known solutions ensure modular installation of the on-off valves, which are designed as identical parts, so that a number of switching functions can be performed with respect to a hydraulic accumulator, despite the compact dimensions of the valve control unit. One on-off valve can actuate the separating element. Another on-off valve can be used for other purposes, for example, to control the gas volume in the gas chamber of the hydraulic accumulator. To the extent that these known solutions are used in overall devices, the other on-off valve can also perform other switching tasks relating to adjacent fluid-bearing units, for example, in the form of cooling pumps, hydraulic cylinder devices, etc.
Since the switching direction of the on-off valves runs or extends parallel to the direction of motion of the separating element as well as in the longitudinal direction of the hydraulic accumulator, it is possible to control the flows of fluid in ways that are favorable from the standpoint of fluid mechanics without diverting the flows. Since the on-off valves are designed as identical parts, the valve control unit and also the hydraulic accumulator can be designed in a very cost-effective manner. If a certain on-off valve is not required for a certain use of the hydraulic accumulator, this valve can also be simply left out of the design and the recess can be closed off with a filler plug. Alternatively, this valve can be used in other ways to guide the fluid. If the actual hydraulic accumulator or its valve control unit fails, these devices can be readily detached from one another and replaced with new components so that the overall function of the hydraulic system in the application of the hydraulic accumulator is not put at risk.
With the solutions of this type, the on-off valves are connected to the corresponding hydraulic accumulator as detachable parts. Sealing problems can arise, and mechanical stress, for example, can cause the respective valve control unit to be separated or torn away from the accumulator housing.